In contrast to previous practice, tests are nowadays frequently performed not on site, which is to say directly on a specimen, but from another location, which is to say under remote control. This involves the eventuality that data, in particular measurement results, may become corrupted on the transmission link between the control unit and specimen, especially when the data is transmitted in accordance with a transmission protocol used for the unsecured transmission of data. This means that a secured statement as to whether the measurement result reflects the actual situation on the specimen is not possible.
An example of a transmission protocol used for the unsecured transmission of data is the User Datagram Protocol, or UDP for short. UDP dispenses with error detection and correction, which is why processing of the data packets takes less time. A data packet also has a smaller header and hence a better useful data to packet length ratio.
UDP is thus better suited to applications that send short messages and repeat them in full when necessary, or to applications executed in realtime. The entire error-correction process therefore takes place within the application programs. This relates not only to bit errors but also to the total loss of the data packets, because routers will immediately reject UDP datagrams in the event of a high network load.
For the reasons cited, a complex method is required for securing the data within the control unit and specimen.